The present invention relates to a process for producing an electrophotographic photoreceptor that has a light-sensitive layer coated on an electroconductive base. More particularly, the invention relates to a process by which electrophotographic photoreceptors of high quality can be manufactured for a long term without experiencing variations in their characteristics. The invention also relates to the electrophotographic photoreceptor that is produced by that process.
Various inorganic and organic photoconductive materials are known to be useful in electrophotographic photoreceptors. Organic photoconductive materials as applied to electrophotography have several advantages such as high film transparency, good film forming property, flexibility and low cost.
With a view to improving the sensitivity and durability of photoreceptors that use organic photo-conductive materials, a double-layer type has been proposed that has the light-sensitive layer divided functionally into a charge generation layer and a charge transport layer. In a typical case, the charge generation layer is formed by first preparing a coating solution that has a charge generation material dissolved in a suitable solvent together with a binder resin and any necessary additives, then applying the solution to a conductive base and finally drying the applied coat. Similarly, the charge transport layer is formed by first preparing a coating solution that has a charge transport material dissolved in a suitable solvent together with a binder resin and any necessary additives, then applying the solution to the already formed charge generation layer, and finally drying the applied coat. If necessary for improving the adhesion of the applied coat and the charge retaining ability, a subbing layer may sometimes be applied and dried between the base and the light-sensitive layer. The respective coating solutions used in this particular case are typically prepared in separate steps and supplied individually to the application and drying steps.
The subbing layer, the charge generation and the charge transport layer can be applied by various coating methods including blade coating, wire bar coating, spray coating, dip coating, bead coating, curtain coating, air knife coating, rod coating, applicator coating, web coating and gravure coating. The applied coatings of subbing layer, charge generation layer and charge transport layer can be dried by various known techniques including the blasting of hot air as produced by heating atmospheric air and exposure to electromagnetic waves such as infrared rays and electron beams.
The above-stated process for the manufacture of electrophotographic photoreceptors has involved the problem that variations in the quality of coating solutions occur in the step of their preparation to affect the characteristics of the photoreceptor as the final product. In other words, preparing coating solutions from the same materials by the same processing method will in no way assure consistency in the quality of the coating solutions and this has made it difficult to manufacture electrophotographic photoreceptors having consistent characteristics.
Furthermore, using production equipment that employed devices for applying the coating solutions and drying the applied coatings in accordance with the steps described above, the present inventors produced a lot of electrophotographic photoreceptors on a continuous basis for a prolonged term and conducted close studies on the characteristics of those photoreceptors. As it turned out, even in a one-day production, some photoreceptors had high photosensitivity while others had low sensitivity. When the production continued for several days, variations occurred on different days of coating application. Significant variations are also frequent in a one-year production. These variations affected the performance of the electrophotographic photoreceptors as the final product, making it impossible to manufacture photoreceptors having consistent characteristics. Thus, the adverse effects of the variations on the quality of the final product have been a great concern to the manufacturers of photoreceptors.
The present invention has been accomplished under these circumstances and has as an object providing a process by which electrophotographic photoreceptors having consistent characteristics can be manufactured continuously for a long period of time.